Conventional echo ranging techniques have been used to detect the presence of, determine the position of, and measure the distance of moving objects. In such systems, ultrasonic waves, having a predetermined frequency, are transmitted towards and are reflected by the moving object. Additionally, these systems may further employ a stationary reference at a fixed distance from the transmitter. This stationary reference is operative to reflect the transmitted waves. The position of the moving object is then calculated by comparing the elapsed time of the reflections from the stationary reference to the elapsed time of the reflections from the moving object.
Such systems are subject to the effects of false echoes and other unwanted signals because the window to read the target reflection must be large enough to accommodate the full range of the distance measured. A need therefore exists to reduce the window necessary to read the target reflection and thereby minimize or eliminate the effects of false echos.